Factors and Processes Controlling the Duration of Concentric Eyewall Structure and the Associated Intensity Change of Tropical Cyclones

University Of Hawaii, Honolulu

Investigators

Abstract

The eyewall replacement cycle (ERC) in tropical cyclones consists of the formation, contraction and intensification of the outer eyewall and the weakening and dissipation of the inner eyewall. The ERC is critical for forecasting the impacts of tropical cyclones because it is usually accompanied by a short-term weakening of the tropical cyclone with an expansion of the wind field. This project will focus on the formation of the outer eyewall and the length of time that it takes to complete the cycle. The award will also provide training for a graduate student. This project will identify key factors and processes that control the duration of the ERC and the associated intensity change based on both diagnostics of idealized high-resolution numerical simulations and analysis of digitized satellite observations and tropical cyclone best-track data. The primary hypothesis guiding the work is that the timescale of the ERC is controlled primarily by the width of the moat between the primary and secondary eyewalls and the intensification and contraction rates of the outer eyewall. Four primary research tasks will be performed: 1) Examine how the structure and intensity of the initial tropical cyclone-like vortices affect the timescale of ERC and the associated intensity change in a given quiescent environment, 2) Examine how the timescale of ERC and the associated intensity change may vary with SST, environmental relative humidity, and background rotational rate, 3) Examine how the environmental asymmetric forcings may affect the timescale of ERC and the associated intensity change, such as the beta-effect, environmental flow, and vertical wind shear, and 4) Verify the above findings by analyzing a publicly available concentric eyewall dataset and a tropical cyclone database and to construct a regression model for the duration and intensity change of ERCs using identified factors. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.